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Thread: Materials in Return Air Plenum

  1. #1
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    Materials in Return Air Plenum

    2006 IBC, IMC.

    Major remodel of a single story building w/ full basement, non sprinklered, type V-B, proposed B occupancy. The ceiling space between the T grid and the upper ceiling floor assembly has been and will be used as a return air plenum.

    The place was built in the late 80's. It is not a change of occupancy.

    The entire ceiling of the basement is insulated with fiberglass kraft/foil faced insulation. It is fullly exposed, with no ignition barrier (it states right on it that it must be covered w/approved building material).

    I will be contacting the contractor tomorrow to let him know that it will not be approved to leave the insulation there as it is.

    He will probably propose covering it with a foil faced or white paper vapor barrier that has the required flame spread etc. What I don't know is if the kraft paper should be removed first, or if it will be acceptable to simply cover it with another vapor barrier.

    The purpose of the insulation is for sound only (as far as I know at this point).

    I don't recall the brand of the insulation, but it is 20+ years old. I will find out the brand and see if I can find out what an approved covering is as far as they are concerned.

    Anyone out there run into this in their past?

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    Check IMC section 602.2.1. By exception 5, the only way to cover non-plenum rated materials in a plenum is with either a drywall assembly or with materials specifically listed and labeled for covering items in a plenum. The only listed material I know of is a plenum wrap similar to the fire wrap used on grease duct. The only thing I see it used for is covering pvc pipe. Not sure, but I think covering pipe is about the only application it's listed for. I would guess they'll either have to cover the old insulation with drywall or use a ducted return.

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    Be prepared for the following argument (not saying it's valild, it just is):

    IMC 602.2 states "Plenum enclosures shall be constructed of materials permitted for the type of construction classification of the building". In VB, wood is allowed, so all they have to do is strip off the insulation and it is legal to have wood be the construction material for the plenum. Or even better, insulated wood is allowed in VB, so as long as an ignition barrier is added, the construction of the plenum meets the requirements for a VB.

    All I can see the insulation doing is maybe reduce footfall sounds.

    Agree that as-is is as it shouldn't be.

  4. #4
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    Don't over think this if the insulation meets ASTM E 84 then it would be ok.

    602.2.1 Materials exposed within plenums.
    Except as required by Sections 602.2.1.1 through 602.2.1.5, materials within plenums shall be noncombustible or shall have a flame spread index of not more than 25 and a smoke-developed index of not more than 50 when tested in accordance with ASTM E 84.
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    I'm not too concerned about the fiberglass itself. The vapor barrier is my concern. It is not only flamable, but highly flamable. It has a sort of "tar" in it that does not meet flame spread, etc.

    It says right on it that it is not to be left exposed.

    I wouldn't pass it even if it wasn't in the plenum. The only way this can be installed properly is if it is covered with an approved building material, plenum or no plenum.

    I have an inquiry into Owens Corning concerning the matter.
    Last edited by Glennman CBO; June 16th, 2010 at 21:11.

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    you're putting combustibles and potential toxins in a combustible building with potential toxins (OSB, any PVC).. remove the kraft paper (fiberglass has it's own health hazards)..
    (PE)ach
    some days are just that..

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    Thanks peach. I have yet to hear from Owens Corning. The contractor's job is basically on hold. I told him today that his designer will be required to propose a fix, and our department will have to review it.

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    bad existing construction.. make whatever improvements you can get!
    (PE)ach
    some days are just that..

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    An update. I finally received a response from Owens Corning. They said that either the paper would need to be removed, they can reverse the insulation (the vapor barrier is not actually functioning as such), or they can cover it with a 15 minute material.

    They are proposing covering it with a 15 minute FSK.

    I know what FSK is, but I didn't know there was a 15 minute FSK.

    I have yet to see some cut sheets.

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